It is well established that metastatic tumor cells are present in blood and bone marrow throughout the course of cancer disease (1-4). These circulating tumor cells (CTCs) are thought to seed the disease and distant metastases in the body (5,6). Isolating and characterizing the CTCs could provide invaluable information for diagnosis, treatment and prognosis of different stages of cancer (2,3,7). The concentration of CTCs in blood is typically low and can be as low as 1 cell/ml of blood (8). An ideal isolation technique has to be able to specifically capture and isolate single CTCs from billions of blood cells with close to 100% efficiency, without significant contamination by non-specific cells. We propose to use targeted microbubbles (hereafter [unreadable]bubbles) to develop a method for isolation and analysis of rare tumor cells. [unreadable]Bubbles could offer potential advantages over magnetic beads as a cell isolation technique. We show in our preliminary data that targeted [unreadable]bubbles efficiently attach to their target cells in blood, so that the cells become buoyant and easily separate from all other cells using gravity/centrifugation. The goal of this proposal is to test whether the [unreadable]bubble separation can achieve the sensitivity of magnetic bead separation, but with higher specificity, speed and productivity (ability to process >10 ml blood). These goals are achievable within the time frame of this award to allow us to assess whether further development is warranted. PUBLIC HEALTH RELEVANCE: To develop and to test tumor cell isolation technique for diagnosis of cancer. The technique will be based on the use of gas microbubbles that will attach to metastatic tumor cells in blood sample and will separate by buoyancy.